Drossing fluxes



United States Patent 0 DROSSING FLUXES Frederick Molesworth Bunbury and Francis Walter Pursall, Birmingham, England, assiguors to Foundry Services Limited, Birmingham, England, a British com- P y No Drawing. Application December 31, 1956 Serial No. 631,454

Claims priority, application Great Britain January 2, 1956 10 Claims. (Cl. 75-94) The present invention relates to the melting of metals and is more particularly concerned with improvements in drossing fluxes for use in the melting of light alloys, e. g. alloys containing aluminium, magnesium and other metals of low melting point.

During the melting of light alloys, particularly those based upon or containing a substantial proportion of aluminium, the molten metal surface becomes covered with a powdered mixture of oxides and entrapped globules of metal. This mixture, which is known as dross, has to be skimmed from the metal surface prior to casting and can constitute a serious loss of metal since it often contains as much as 50 to 70% of metal particles. Consequently, efforts have been made to develop fluxes which enable the separation of the metal from the oxide in the dross prior to skimming.

The most satisfactory fluxes known for this purpose are based upon fluorides. The fluorides enable the fine aluminium particles in the dross to ignite with the evolution of heat. This exothermic reaction, coupled with the presence of fluoride salts from the flux, enables the metal particles to coalesce, so that they separate back into the metal bath from the dross.

This evolution of heat requires an intimate mixing or rabbling of the flux into the dross, and even then it is diflicult to obtain an exothermic reaction at temperatures below about 750 C. For die casting work, particularly pressure die casting, where temperatures of about 600 C. are quite usual, the temperature is not sufficiently high to enable ignition of the fine metal particles in the dross to take place.

It is an object of the present invention to produce a satisfactory exothermic reaction at low temperatures and to overcome the necessity for excessive rabbling of the flux into the dross with consequent fatigue upon operators.

According to the present invention, a drossing flux for use with light metals comprises a fluoride and aluminium in fine particulate form in quantity sufficient to lower the temperature of the exothermic reaction between the flux and the dross. Any of the fluorides commonly employed in drossing fluxes may be employed, e. g. alkali metal fluorides, calcium fluoride, sodium aluminium fluoride, potassium aluminium fluoride, sodium borofluoride, potassium borofluoride and alkali metal silico-fluorides. The flux may advantageously contain other fluxing salts in addition, e. g. sodium or potassium sulphates or chlorides.

It has been found that fine aluminium powder of approximately minus 300 mesh size, available commercially as aluminium paint powder, enables a good reaction to be obtained in a dross at about 600 C. even when only about 3% of the paint powder is incorporated into the fluoride-containing flux. This same flux without the aluminium powder only reacts at about 700 C.

It has also been found that coarser particles of aluminium powder can give satisfactory results but somewhat larger quantities are required and the reaction temperature is not reduced to such a marked extent. For example the incorporation of 15% of a blown aluminium powder Example The following flux has been found to give satisfactory separation of metal from dross produced in melting aluminium alloys:

Percent Fine aluminium powder (minus 300 mesh) 3 Various fluorides, including cryolite and sodium silicofluoride (sodium chloride and sulphate) 35 Inorganic salts 62 It will be understood that the invention includes not only the drossing fluxes hereinbefore set forth but also a method of treating light metals and alloys thereof which comprises adding to the molten light metal a drossing flux as set forth.

What we claim is:

l. A drossing flux for use with light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises aluminium of particle size minus 200 mesh and a fluoride, the ingredients of the composition not being of themselves exothermically reactive with one another.

2. A drossing flux for use with light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises aluminium of particle size minus 300 mesh and a fluoride, the ingredients of the composition not being of themselves exothermically reactive with one another.

3. A drossing flux for use with light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises aluminium of particle size minus 300 mesh and sodium aluminium fluoride, the ingredients of the composition not being of themselves exothermically reactive with one another.

4. A drossing flux for use with light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises aluminium of particle size minus 300 mesh and alkali silico fluoride, the ingredients of the composition not being of themselves exothermically reactive with one another.

5. A drossing flux for use with light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises aluminium of particle size minus 300 mesh a fluoride and a fluxing salt selected from the class consisting of sodium and potassium chlorides and sulphates and mixtures thereof, the ingredients of the composition not being of themselves exothermically reactive with one another.

6. A method of treating light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises adding to the molten metal a drossing flux as claimed in claim 1.

7. A method of treating light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises adding to the molten metal a drossing flux as claimed in claim 2.

8. A method of treating light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises adding to the molten metal a drossing flux as claimed in claim 3.

9. A method of treating light metals selected from the class consisting of aluminium, magnesium and alloys of either, which comprises adding to the molten metal a drossing flux as claimed in claim 4.

10. A method of treating light metals selected from the class consisting of aluminum, magnesium and alloys of ither, which comprises adding to the molten metal a 2,578,977 Lytle Dec. 18, 1951 dressing flux as claimed in claim 5. 2,591,105 Strauss et al. Apr. 1, 1952 f 2,760,859 Graf Aug. 28, 1956 Zififififili 1028 216 H E t T N J 4 1912 5 247,149 Great Britain Feb. s, 1925 omane a. une 1,066,833 McClenahan July 8, 1913 OTHER REFERENCES 2,162,938 Comstock et al. June 20, 1939 Journal of the Institute of Metals, vol. 75, part 6, 194-9,

2,490,327 Sotfel Dec. 6, 1949 10 page 470, Emleys article. 

2. A DROSSING FLUX FOR USE WITH LIGHT METALS SELECTED FROM THE CLASS CONSISTING OF ALUMINIUM, MAGNESIUM AND ALLOYS OF EITHER, WHICH COMPRISES ALUMINIUM OF PARTICLE SIZE MINUS 300 MESH AND A FLUORIDE, THE INGREDIENTS OF THE COMPOSITION NOT BEING OF THEMSELVES EXOTHERMICALLY REACTIVE WITH ONE ANOTHER. 